Apparatus for electrostatically coating articles



y 0, 1950 H. P. RANSBURG ETAL 2,509,448

APPARATUS FOR ELECTROSTATICALLY COATING ARTICLES Filed June 28, 1944 2 sheets-sheet 1 y 30, 1950 H. P. RANSBURG ETAL 2,509,448

APPARATUS FOR ELECTROSTATICALLY COATING ARTICLES Filed June 28, 19 44 2 Sheets-finest 2 1 through the coating zone.

cludes a high-voltage source, preferably unidirec-n Patented May 30, 1950 UNITED STATES I PATENT OFFICE APPARATUS FOR ELECTROSTATICALLY COATINGABTICLES Harold P. Ransburg and Norman S. Curtis, Indianapolis, Ind., auignors, by mesne assignments, to Bansburg Elcctro-Coating Corp., Indianapolis, Ind., a corporation of Indiana Application June 28, 1844, Serial No. 542,558

This invention relates to the electrostatic coating of articles, and more particularly to the application of liquid coating materials to articlesurfaces, such for example as interior surfaces,

which do not lend themselves well to coating by between the electrode and the articles whereby the coating-material particles acquire a charge opposite to that of the articles and are electrostatically urged theretoward. Where the articles are of such shape, and the stationary electrode can be so formed, that an adequate supply of charged coating-material particles can be maintained over all portions of the surface or surfaces being coated, such method functions very satisfactorily. But in other situations, as in the coating of interior surfaces, it is frequently difficult or impossible to obtain with stationary electrodes and guns the distribution of charged particles and the pattern of electrostatic forces necessary to the production of a satisfactorily uniform coating.

It is accordingly an object of this invention to provide an apparatus for electrostatically coating surfaces, such as interior surfaces of articles, which can be satisfactorily coated only with difficulty by previously known electrostatic coating apparatus. Another object of the invention is to provide, in electrostatic coating apparatus, an automatic control means operative to prevent the discharge of coating material and the application of potential differences except when one i or more-articles are in proper position for coating.

In carrying out the invention in its preferred form, we employ a conveyor for successively moving the articles to be coated through a coating zone, but instead of employing a stationary electrode as in prior apparatus, we mount the electrode for movement and provide means for bringing it into and maintaining it in proper co-operatlve relationship with each article passing The apparatus intional, and automatic mechanism for rendering it operative to-maintaln a substantial difference of 18 Claims. (CI. 91-18) electrical potential between the movable electrode and the associated article as the latter is being coated. Coating-material supply means, such as an air-atomizing spray gun, is provided for supplying the coating material which is to be electrostatically deposited, such means conveniently being movable with the electrode and under con-- trol of the automatic mechanism so as to be operative only when the electrode is in proper co-mperative association with an article. If the articles to becoated are sufficiently conducting in character they may be connected to one terminal of the high-voltage source as through the conveyor which moves them through the coating zone, but otherwise each article has associated with it a backing electrode which is connected to the highvoltage source. Because each article may either be itself connected to the voltage source or may have associated with it a backing electrode so connected, the articles are hereinafter referred to as comprising collecting electrodes, and to distina guish the oppositely charged movable electrode it is hereinafter referred to as a discharge electrode. If desired, there may be a group of: discharge electrodes and spray guns movable as a unit and so arranged as to co-operate respectively with a plurality of articles in the coating zone.

The full nature of the invention will be understood from the accompanying drawings and the following description and claims:

Fig. 1 is a perspective view showing the apparatus in spray coating position. Fig. 2 is a sectional view through one of the containers including its support and coating apparatus. Fig. 3 is a wiring diagram illustrative of the operating electrical circuits.

In the drawings for the purpose of illustrating a preferred embodiment of the invention, there is shown a continuously moving conveyor 10 upon which a series of articles II is supported, while the interior surfaces thereof are electrostatically coated with a material such as paint, lacquer or the like. The containers are centered on and car ried by a rotatable platform I2 mounted on a spindle l3 having its bearing on the conveyor [0. The lower end of said spindle is provided with a pinion l4 engageable with the teeth of a rack bar l5. Thus, as the article is caused to move with the conveyor, it will be rotated through the rack and pinion engagement at a prescribed speed of rotation. This is for the purpose of bringing the entire inner surface of the article into the direct path of the spray of coating material.

A plurality of discharge electrodes l6 of approspaced intervals by a supporting frame I! which in turn is supported by a hanger I8 from an overhead trolley l9 riding upon a Supporting track 20. Said hanger I8 is vertically slidable in a carriage 2| mounted upon traction wheels 22 movable along a track 23. Mounted above the track 23 there is provided a spiral drive shaft 24 rotatably mounted at each end in the bearings 25 on said track. Said shaft is driven through the bevel gears 26 at one end thereof which in turn are driven by a shaft 2! carrying a sprocket 28. Said sprocket is driven by a driving chain 29 which is driven in timed relation with the conveyor I D from a suitable source of power not shown. The shaft 24 is provided with opposed spiral grooves 30 engageable by a pin in the carriage 2 i, the said spiral grooves being connected adjacent opposite ends of the shaft to efiect reciprocable movement of the carriage back and forth from one end to the other. Said spiraled grooves are so formed on the shaft that with the rotation thereof in timed relation to the movement of the conveyor and articles carried thereby, the carriage and electrodes it will be caused to move with the containers from the left-hand end of the shaft to the right-hand end thereof.

The track 2b is provided with a lower transverse portion A connected with an upper trans- I verse portion B by an elevating portion at one end and a lowering portion D at the other end thereof. At the junction between portions C and A B of the track there is a downwardly springpressed switch plate 3i and at the junction of the portion B with the portion D there is an upwardly spring pressed switch plate This arrangement is such that durin the travel of the the trolley through the upwardly inclined portion C, the electrodes will thereby be lifted from the containers. The trolley will then be caused to raise the switch plate 36 and enter the portion .13 of the track to the right-hand side thereof, as indicated by dotted lines.

Upon clearing the switch plate, the electrodes having been thus elevated from the containers, the carriage will have reached the end of its movement in one direction and will be reversed by the spiral groove to thereupon travel in the opposite direction over the switch plate 3!]. In such raised position the electrodes will be carried with the trolley in the direction of the arrow to the opposite end of the track portion B, riding over and depressing the switch plate 32. Havin cleared the switch plate 32, the carriage 2| will be at the left-hand end of the driving shaft and its movement reversed by the spiral groove thereon so that it moves in the same direction and speed as the containers. In so moving, the switch plate 32 being spring elevated, the trolley will ride down track portion D to lower the electrodes into the containers, thereby completing the cycle of movement.

Carried on an auxiliary frame 33 of the frame I! there is provided a spray un 34 adjustably mounted for directing a spray of coating material into the space between the electrode l3 and the inner surface of the article, which space comprises an electrostatic field. As shown herein there is provided a spray gun associated with each electrode, each of said spray guns being connected through flexible tubes 35 with a source of coating material.

The discharge electrodes l6 are connected to a source of high voltage indicated at 36 by a lead-in line 31 leading to a flexible conductor 38 through a spring tension reel 39 mounted on the insulated support 40. The line 38 is connected in series with the electrodes I6 through the spray gun support 33 from which the spray guns are suspended by insulating rods 33a. Similarly, the spray gun support33 is insulated from the frame I! by insulating rods Ila. The articles to be coated comprise the collecting electrode of the system, the conveyor upon which they are carried being grounded, as indicated at 4|. Wherein said articles are of conducting material, they are accordingly grounded and thereby electrically connected through ground to the source of high voltage 36. Wherein said articles are of non-conducting material, they may in efi'ect comprise grounded collecting electrodes by providing a grounded shell about them of conducting material and co-extensive with the sur face to be coated.

The source of high voltage 36 is energized by current from a suitable source 42 supplying 220 volts across the coil of the contactor relay 43 when the switch 44 is closed. This operation shorts the switch 44 so that even though it subsequently opens, the main relay remains closed. It also applies 220 volts to the coil of the solenoid 45 which operates the air lines 35 which in turn operate the spray guns. Simultaneously it applies 220 volts to the primary 46 of the source of voltage 336. This induces a high voltage in the secondary ii that is supplied by way of a rectifying tube 48, lead-in line 31 and the flexible line 38 to the electrodes Hi. This high voltage establishes an electros atic field between the discharge electrode i6 ani the collecting electrode comprising the article which is grounded, current passing through the common ground to the transformer secondary 4'1.

Switch 4 3, which is normally open, is located at the forward end of the portion A of track 20 adjacent its junction with portion D. At the opposite end of portion A there is located a switch 49, which is normally closed, adjacent the junction with the portion C. Switch 44 is actuated to closed position by the trolley 19 upon the electrodes being lowered into operative position within the articles, as shown in Fig. 1. This has the eifect of closing the circuit through relay 43 which closes the circuits from the source of current supply to the air control solenoids "35 through the relay 45 and a similar circuit to the primary 46 for energizing the source of high voltage 36. Thus, upon said switch 44 being closed, an electrostatic field is established between each of the electrodes and its associated article with the simultaneous discharge of coating material from the guns 34. The spraying operation continues as the battery of electrodes with their spray guns and the articles travel with the conveyor l0 until the trolley 59 actuates switch 49. Thereupon the circuit through relay 43 is broken, which in turn breaks the circuits to the relay 45 controlling the spray guns and the primargc-M controlling the source of high voltage. The pinions I4 are of such diameter that during the coating operation each container will be rotated through at least. one complete revolution, so that the entire inner surface thereof will be coated. The spray guns are then cut off and the electrodes de-energized immediately followed by their elevation from within the containers as the trolley proceeds up the portion C of the track.

Thus, the spray cycle is controlled entirely in accordance with the speed and travel of the conveyor I0 and the location of switches 44 and 4!, the trolley with the electrodes and guns carried thereby moving in step therewith. As the electrodes are elevated clear of the articles sprayed. the articles pass on while the trolley and carriage return the battery of electrodes and guns to initial position through portion B of the track.

A new series of articles have in the meantime been conveyed into position for receiving the electrodes and guns as they are again lowered into operative position. They are then caused to function for coating the articles as the articles travel throughout the stretch of the conveyor ll corresponding to the distance between the switches 44 and 49. This cycle is repeated continuously as successive groups of articles are brought by the conveyor into position to have their interior surfaces coated.

The invention claimed is:

1. Apparatus for electrostatically coating the surface of an article wherein said article comprises a collecting electrode, including a discharge electrode associated with the article and spaced therefrom to provide an electrostatic field therebetween, a, source of high voltage having its opposite terminals electrically connected to said electrodes respectively to energize said field, means for moving said articles into and out of coating position, a spray gun positioned on said apparatus to direct a spray of coating material into said field for electrostatic deposition upon the surface of the collecting electrode, switch means for energizing and substantially completely de-energizing the electrostatic field in the zone about the coating position, means for electrically controlling the discharge of the coating material from said gun, an electric control circuit for said control means, switch means in the circuits to said highvoltage source and gun, and switch control mechanism operable to actuate said switches to energize said electrostatic field and render said gun effective when said article is moved into coating position and to de-energize said field and render said gun ineffective upon said article being moved out of coating position.

2. Apparatus for electrostatically coating the surface of an article wherein said article comprises a collecting electrode, including discharge electrode associated with said article and spaced therefrom to provide an electrostatic field therebetween, a. source of high voltage having its opposite terminals electrostatically connected to said electrodes respectively to energize said field. a low-voltage circuit for actuating said high-voltage source means for moving said articles through a predetermined path, a spray gun positioned on said apparatus to direct a spray of coating material into said field for electrostatic deposition upon the surface of the collecting electrode, means for electrically controlling the discharge of the coating material from said gun, anelectric control circuit for said control means, switch 3. Apparatus for electrostatically coating the surface of an article wherein said article comprises a collecting electrode, including a continuously moving conveyor for said article, a discharge electrode, a movable support for said 'discharge electrode, mechanism operable to periodically move said support to position said electrode in cooperative spaced relation to said article and remove it therefrom in timed relation with the movement of said conveyor, 9. source of high voltage having its opposite terminals electrically connected with said electrodes respectively to establish an electrostatic field therebetween, and a means carried by said apparatus to direct a spray of coating material into said field, whereby said material will become charged and attracted for deposition over said surface.

4. Apparatus for electrostatically coating a surface 0! an article wherein said article comprises a collecting electrode. including a discharge electrode, a movable support for. said discharge electrode, mechanism operable to move said support to position said electrode cooperative in spaced seated relation to said article and. remove it therefrom after a predetermined time interval, a source of high voltage having its opposite terminals electrically connected with said electrodes respectively to establish an electrostatic field therebetween. an automatically actuated spray gun carried by said support and movable therewith into and out of operative position to direct a spray of coating material into said field, switch controlled circuits for said source of high voltage and spray gun, and switches in said circuits operable by said mechanism to render said source of high voltage and spray gun effective upon said discharge electrode and gun being moved to operative position and ineffective upon being moved out of operative position.

a 5. Apparatus for electrostatically coating a means in .said low-voltage and control circuits and switch control mechanism operable in timed relation with the movement of said article to actuate said switches to render said gun and electrodes effective when said article is brought to one position and ineffective upon said article going moved through said path to another posisurface of an article wherein said article comprises a collecting electrode, including a continuously moving conveyor for said article, a discharge electrode, a movable support for said discharge electrode, mechanism operable to periodically move said support to position said electrode in cooperative spaced relation to said article and remove it therefrom in timed relation with the movement of said conveyor, a source of high voltage having its opposite terminals electrically connected with said electrodes respectively to establish an electrostatic field therebetween, an electricallyactuatcd spray gun carried by said support and movable therewith into and out of operative position to direct a spray of coating material into said field, switch controlled circuits for said source of high voltage and. spray gun. and switches in said circuits operable by said mechanism to render said source of high voltage and spray gun effective upon said discharge electrode and gun being moved to operative position and ineffective upon being moved out of operative position.

6. Apparatus ibr electrostatically coating 9. surface of an article wherein said article comprises a collecting electrode, including a continuously moving conveyor for said article, a discharge electrode, mechanism operable in timed relation with said conveyor for moving said discharge electrode in cooperative spaced relation to said article during a portion of its travel with said conveyor, 9. source of high voltage having its .opposite terminals electrically connected with said electrodes respectively to establish an elec trostatic field therebetween, and a spray gun associated with said discharge electrode movable therewith into operative position to direct a spray of coating material into said field during the travel of said article in association with said discharge electrode.

7. Apparatus for electrostatlcally coating 9. surface of an article wherein said article comprises a collecting electrode, including a continuously moving conveyor for conveying said article through a coating zone, a discharge electrode, a spray gun, a movable support for said discharge electrode and spray gun, driving mechanism operable in timed relation with said conveyor for moving said support'therewith during the travel of said article through said zone and returning it to initial position, mechanism for moving said support transversely of the direction of conveyor movement to position said electrode in cooperative relation to said article and spray gun in position to direct a coating over the surface thereof to be coated when the article enters the coating zone, said mechanism being operable to move said support with said electrode and spray gun free of said article upon said article reaching the end of its travel through said zone, a source of high voltage having its opposite terminals electrically connected with said electrodes respectively to establish an electrostatic field therebetween, whereby said coating material will become charged and attracted for deposition over said surface during said predetermined travel of said article through said zone, and control mechanism for said source of high voltage and said spray gun operable to render them eilfective while traveling with said article through said zone and ineffective upon being moved free of said article and returned to initial position.

8. Apparatus for electrostatlcally coating the, I

interior surface of a series of articles wherein said articles comprise collecting electrodes, including a continuously moving conveyor for conveying said articles as a group through a coating zone, a battery of discharge electrodes, one for each of said group of articles, a spray gun associated with each of said electrodes, a movable support for said battery of electrodes and spray guns, a track and trolley thereon connected with said support for raising and lowering said battery of electrodes into and out of each succeeding group of article entering into and passing from said zone on said conveyor, a traversing carriage slidably connected with said support, and a drive shaft operable in timed relation with said conveyor for moving said carriage and electrodes with said group of articles during passage through said zone and returning said battery of electrodes to initial position free of said articles to be associated with a following group thereof.

9. Apparatus for electrostatlcally coating the interior surface of a series of article wherein said articles comprise collecting electrodes, including a continuously moving conveyor for conveying said articles as a group through a coating zone, a battery of discharge electrodes, one for each of said group of articles, a spray gun associated with each of said electrodes, a movable support for said battery of electrodes and spray guns, a track and trolley thereon connected with said support for raising and lowering said battery of electrodes into and out of each succeeding group of articles entering into and passing from said zone on said conveyor, a traversing carriage slidably connected with said support, a drive shaft operable in timed relation with said conveyor for moving said carriage and electrodes 'with said group of articles during passage through said zone and returning said battery of electrodes to initial position free of said articles to be associated with a following group thereof, a source of high voltage having its opposite terminals connected with said battery of electrodes and said group of articles respectively through an electric circuit to establish an electrostatic field therebetween into which said coating material is directed by the respective guns, an electric circuit for controlling said guns, and switch means in said circuits operable to simultaneously close said circuits at the beginning of the travel of said electrodes through said zone and break said circuits upon the completion of their travel therethrough.

10. In apparatus for electrostatlcally depositing on each of a series of articles finely divided coating material dispersed in the atmosphere, a conveyor for moving such articles in succession over a predetermined path through a coating zone in which each article is exposed to an atmosphere containing the dispersed, finely divided coating material, a discharge electrode, means operative in timed relation with said conveyor for moving said electrode repeatedly over a closed path in one portion of which the electrode is maintained in co-operative spaced relation with an article passing through said coating zone and in another portion of which the electrode is moved into co-operative spaced relation with a following article, and electrical means including a high-voltage source for creating a suilicient potential diilerence between said discharge electrode and. the article in cooperative relation with it for charging the coating material to a different potential from that of the article to electrostatlcally precipitate the charged coating material on the article.

11. The invention set forth in claim 10 with the addition that said apparatus includes a plurality of discharge electrodes arranged in predetermined spaced relation to each other, said electrode-moving means operating to move said electrodes jointly and repeatedly over paths in portions of which they are maintained in cooperative spaced relation respectively with a group of articles on said conveyor.

12. The invention set forth in claim 10 with the addition of mechanism operated in timed relation with said electrode-moving means for rendering said electrical means operative while said electrode is in the first named portion of its path and inoperative while it is in the last named portion of its path.

13. In apparatus for electrostatlcally depositing a coating material on the surface of an article, means for moving the article through a coating zone, means including a discharge electrode spaced from the article as it passes through the coating zone for creating an electrostatic field overthe surface to be coated, a spray gun, means supporting said spray gun to direct toward a portion of the surface to be coated a jet including finely divided particles of coating material as the article passes through the coating zone, and means for moving said gun cyclicly over a predetermined path in timed relation with movement of said conveyor.

14. Apparatus for electrostatlcally coating the interior surface of an article wherein said article comprises a collecting electrode, including a continuously moving conveyor for conveying said article through a coating zone, a discharge electrode, a movable support for said discharge electrade, a traversing carriage reciprocable over a path generally parallel to the direction of conveyor movement in said coating zone, said support being slidably mounted in said carriage for reciprocation transversely oi the path of carriage reciprocation, a trolley connected with said support, a closed track over which said trolley is caused to move in the reciprocation of said carriage, said track being so shaped as to move said support to position said electrode within an article on said conveyor and subsequently to withdraw the electrode from such article while the carriage is moving in the same direction as the conveyor.

15. In apparatus for electrostatically coating surfaces of a plurality of articles wherein said articles comprise a series of collecting electrodes, including a continuously moving conveyor for conveying said articles in predetermined spaced relation through a coating zone, a battery of discharge electrodes, a common support for supporting said discharge electrodes in spaced relation corresponding to that of articles on the conveyor, means operative cyclicly in timed relation with said conveyor to operate said support to position said discharge electrodes respectively in co-operative spaced relation with a group or articles entering the coating zone, to move the discharge electrodes with such group of articles as they progress through the coating zone, and then to return the electrodes for association with a following group of articles, and a spray gun electrode having, in combination, means for moving said article over a predetermined path through a coating zone, field creating means including a discharge electrode, said means also being electrically associated with said article, a coating material issuing means, means for supporting said discharge electrode and said issuing means, said discharge electrode and issuing means being spaced from each other, and driving means operative upon entry of said article into said coating zone to move said discharge electrode into operative relationship with said article for creating an electrostatic field over the article surface to be coated and to move said issuing means into operative position for coating said surface.

HAROLD P. RANSBURG.

NORMAN S. CURTIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,121,802 Clark Dec, 22, 1914 1,698,845 Gustin Jan. 15, 1929 1,816,903 Hageman et a1. Aug. 4, 1931 1,855,869 Pugh Apr. 26, 1932 1,889,676 Little Nov. 29, 1932 2,097,233 Metson Oct. 26, 1937 2,124,853 Grupe July 26, 1938 2,128,327 Russell et a1 Aug. 30, 1938 2,217,444 Hill Oct. 8, 1940 2,334,648 Ransburg et a1 Nov. 16. 1943 FOREIGN PATENTS Number Country Date 8,703 Great Britain Apr. 16, 1903 

